Method for displaying selective laser melting pool

Abstract

The invention belongs to the technical field of material microstructure testing, and particularly relates to a method for displaying a selective laser melting pool. The method comprises the following steps: S1, sampling: cutting and sampling a to-be-detected sample to obtain a sample; s2, grinding and polishing: grinding, polishing, cleaning and blow-drying the sample; s3, electrolysis is conducted, specifically, the sample is electrolyzed, and an adopted electrolyte is prepared from ethyl alcohol and perchloric acid according to the proportion; s2, after electrolytic polishing, observing whether over-corrosion exists on the surface of the sample, and if over-corrosion exists, repeating the step S2; s4, electron microscope observation and photographing are carried out, the voltage is 15KV, and secondary electron observation and photographing are carried out on the sample; according to the method, the sample is ground and polished, then the electrolyte of ethanol and perchloric acid is adopted, the polishing voltage is controlled for electrolytic polishing, and meanwhile, a fish scale-shaped molten pool for selective laser melting of the sample can be clearly displayed by selecting a proper diaphragm and a proper focal length and adjusting parameters such as exposure and contrast.

Description

Technical Field

[0001] The invention belongs to the technical field of material microstructure testing, and in particular relates to a method for displaying a molten pool by selective laser melting. Background Art

[0002] Selective laser melting technology is an advanced additive manufacturing method that uses laser as a heat source to sweep and melt metal powder laid layer by layer, so that the metal powder is stacked layer by layer to form a block.

[0003] During the selective laser melting process, a fish-scale molten pool will be formed under the action of laser on metal powder. According to research, due to the fast cooling speed of selective laser melting, the molten pool formed by selective laser melting has obvious differences from the microstructure of aluminum alloy formed by traditional forming methods (such as casting). The molten pool structure no longer has the microstructure characteristics of traditional aluminum alloys such as grains and grain boundaries. The inside and boundary of the molten pool are fish-scale substructures formed by cellular structures. People have found that this substructure of the molten pool consists of three parts: fine grain area, coarse grain area and heat affected zone. Among them, this sub-regional microstructure has a significant impact on the mechanical properties of the material. From a macroscopic point of view, the size and morphology of the molten pool have a decisive influence on the mechanical properties of the metal formed by selective laser melting, such as tensile strength, toughness, and plasticity. In addition, the size and morphology of the molten pool are one of the bases for adjusting the selective laser melting forming process. The display of the molten pool morphology is a basic issue in studying the molten pool morphology. Therefore, the display of the molten pool morphology is of great significance in the analysis of the microstructure of the material.

[0004] Aluminum alloys and aluminum-based composites are a type of lightweight, high-specific-strength, corrosion-resistant structural materials that are widely used in aerospace, rail transit, medical equipment, etc. Aluminum alloys and aluminum-based composites can be used as a selective laser melting material. Certain grades of aluminum alloys have good forming quality and excellent mechanical properties and have been extensively studied.

[0005] At present, Keller reagent is commonly used for etching the microstructure of aluminum alloys and aluminum-based composite materials. However, Keller reagent has a poor display effect on the fish-scale substructure of the molten pool formed by selective laser melting, the molten pool boundary is blurred, and the reaction effect is difficult to control. However, the method proposed in the present invention can display the molten pool characteristics of aluminum alloys and aluminum-based composite materials. The electrolytic display molten pool has the following advantages: parameters can be quantified, the reaction is fast and controllable, the molten pool boundary is clearly displayed, no pollution such as smoke is generated, it can be reused multiple times and is environmentally friendly. Summary of the invention

[0006] In order to solve the above-mentioned technical problems, this application provides the following technical solutions: The present invention provides a method for displaying a molten pool of selective laser melting, comprising the following steps: S11: forming a metal sample by a selective laser melting method and then cutting it to obtain a sample; S12: grinding, polishing, cleaning and drying the sample; S13: electrolyzing the sample dried in step S12, and repeating steps S12 and S13 when the sample after electrolysis is over-corroded; during the electrolysis, the electrolyte includes ethanol and perchloric acid; S14: Observe and take photos of the microstructure of the sample after electrolysis in step 13 without over-corrosion.

[0007] Preferably, the material of the metal sample is selected from aluminum alloy or aluminum-based composite material.

[0008] Preferably, in step S11, a precision cutting machine is used for cutting, and the length, width or diameter of the inspection surface of the sample is 5-10 mm.

[0009] Preferably, in step S12, 400#, 600#, 800# and 1000# silicon carbide sandpaper are used step by step for unidirectional grinding until the previous grinding mark completely disappears.

[0010] Preferably, in step S12, polishing is performed using a diamond suspension until the wear marks completely disappear.

[0011] Preferably, in step S12, the cleaning is performed using running water, followed by rinsing with analytical grade alcohol, and finally drying with cold air.

[0012] Preferably, in step S13, the volume ratio of ethanol to perchloric acid is 9:1.

[0013] Preferably, in step S13, during electrolysis, the electrolyte is frozen at -30°C, the sample is connected to the positive electrode, the lead plate is connected to the negative electrode, and the positive and negative electrodes are 5-10 cm apart.

[0014] Preferably, in step S13, the electrolysis voltage is 10-30 V, and the electrolysis time is 2-8 s.

[0015] Preferably, in step S14, observation and photography are performed using an optical microscope or a scanning electron microscope.

[0016] Furthermore, the voltage of the scanning electron microscope is 15 KV, and secondary electrons are used to observe the sample and take pictures.

[0017] The technical solution of the present invention has the following advantages over the prior art: At present, Keller reagent is commonly used for etching the microstructure of aluminum alloys and aluminum-based composite materials. However, Keller reagent has a poor display effect on the fish-scale substructure of the molten pool formed by selective laser melting, the molten pool boundary is blurred, and the reaction effect is difficult to control. However, the method proposed in the present invention can display the molten pool characteristics of aluminum alloys and aluminum-based composite materials. The electrolytic display molten pool has the following advantages: parameters can be quantified, the reaction is fast and controllable, the molten pool boundary is clearly displayed, no pollution such as smoke is generated, it can be reused multiple times and is environmentally friendly.

[0018] By adopting the present invention, after grinding and polishing the sample, an electrolyte of perchloric acid + ethanol is used, and the polishing voltage and time are controlled for electrolysis. At the same time, by selecting a suitable aperture, focal length, and adjusting parameters such as exposure and contrast, the laser melting molten pool of the selected area of ​​the sample can be clearly visible. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The molten pool morphology characteristics of AlSi10Mg shown by the present invention are adopted; Figure 2 The morphological characteristics of the AlSi10Mg molten pool under high magnification displayed by the present invention; Figure 3 This is the corrosion effect of AlSi10Mg using Keller reagent; Figure 4 This is the principle diagram of selective laser melting; Figure 5 A flow chart of the method for selective laser melting of a molten pool according to the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention. Example 1

[0021] A method for displaying a molten pool of selective laser melting, comprising the following steps: Step S0: selective laser melting to form AlSi10Mg sample; Step S1: Sampling, cutting and sampling the AlSi10Mg to be tested to obtain a test sample; Step S2: grinding and polishing, grinding and polishing the sample; using 400#, 600#, 800# and 1000# silicon carbide sandpaper for unidirectional grinding step by step until the previous grinding mark completely disappears.

[0022] Step S3: electrolysis, electrolyzing the sample, using an electrolyte ratio of 90 mL ethanol and 10 mL perchloric acid; the voltage is 30 V, and the electrolysis time is 2 s; after electrolysis, observe whether there is over-corrosion on the surface of the sample, if there is over-corrosion, repeat step S2; Step S4: Observe and take photos, using an optical microscope or a scanning electron microscope to observe the microstructure and take photos. Example 2

[0023] A method for displaying a molten pool of selective laser melting, comprising the following steps: Step S0: Selective laser melting to form a TiB2 / AlSi10Mg sample; Step S1: Sampling, cutting and sampling the TiB2 / AlSi10Mg to be tested to obtain a test sample; Step S2: grinding and polishing, grinding and polishing the sample; using 400#, 600#, 800# and 1000# silicon carbide sandpaper for unidirectional grinding step by step until the previous grinding mark completely disappears.

[0024] Step S3: electrolysis, electrolyzing the sample, using an electrolyte ratio of 90 mL ethanol and 10 mL perchloric acid; the voltage is 15 V, and the electrolysis time is 3 s; after electrolysis, observe whether there is over-corrosion on the surface of the sample, if there is over-corrosion, repeat step S2; Step S4: Observe and take photos, using an optical microscope or a scanning electron microscope to observe the microstructure and take photos.

[0025] Comparative Example 1 A method for displaying a molten pool of selective laser melting, comprising the following steps: Step S0: selective laser melting to form AlSi10Mg sample; Step S1: Sampling, cutting and sampling the AlSi10Mg to be tested to obtain a test sample; Step S2: Grinding and polishing: Grinding and polishing the sample; using 400#, 600#, 800# and 1000# carbonized ming Step S3: Keller reagent etching, with a ratio of (95 mL H2O, 2.5 mL HNO3, 1.5 mL HF) for chemical etching; after etching, observe whether there is over-corrosion on the surface of the sample. If there is over-corrosion, repeat step S2; Step S4: Observe and take photos, using an optical microscope or a scanning electron microscope to observe the microstructure and take photos.

[0026] Effect analysis Figure 1The molten pool morphology characteristics of AlSi10Mg shown by the present invention can be seen, and the obvious arc-shaped molten pool edges overlap each other to form a fish-scale molten pool morphology. This is because the selective laser melting uses laser as a heat source to act on the powder layer by layer to form a molten pool. Figure 2 It is an enlarged view of the molten pool, and the molten pool can be further studied based on the morphology of the molten pool boundary and the cellular structure inside the molten pool. Figure 3 This is the effect after corrosion using Keller's reagent, and the magnification is Figure 1 Similarly, it is difficult to clearly show the obvious molten pool edge and fish-scale molten pool morphology at this magnification.

[0027] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for displaying a molten pool of selective laser melting, characterized in that: The steps include: S11: forming a metal sample by a selective laser melting method and then cutting it to obtain a sample; S12: grinding, polishing, cleaning and drying the sample; S13: electrolyzing the sample dried in step S12, and repeating steps S12 and S13 when the sample after electrolysis is over-corroded; during the electrolysis, the electrolyte includes ethanol and perchloric acid; S14: Observe and take photos of the microstructure of the sample after electrolysis in step 13 without over-corrosion.

2. The method for displaying a molten pool by selective laser melting according to claim 1, characterized in that: The material of the metal sample is selected from aluminum alloy or aluminum-based composite material.

3. The method for displaying a molten pool by selective laser melting according to claim 1, characterized in that: In the step S11, a precision cutting machine is used for cutting, and the length, width or diameter of the inspection surface of the sample is 5-10 mm.

4. The method for displaying a molten pool by selective laser melting according to claim 1, characterized in that: In step S12, 400#, 600#, 800# and 1000# silicon carbide sandpaper are used step by step for unidirectional grinding until the previous grinding mark completely disappears.

5. The method for displaying a molten pool during selective laser melting according to claim 1, characterized in that: In step S12, polishing is performed using a diamond suspension until the wear marks completely disappear.

6. The method for displaying a molten pool during selective laser melting according to claim 1, characterized in that: In step S13, the volume ratio of ethanol to perchloric acid is 9:

1.

7. The method for displaying a molten pool during selective laser melting according to claim 1, characterized in that: In the step S13, during electrolysis, the electrolyte is frozen at -30°C, the sample is connected to the positive electrode, the lead plate is connected to the negative electrode, and the positive and negative electrodes are 5-10 cm apart.

8. The method for displaying a molten pool during selective laser melting according to claim 1, characterized in that: In step S13, the electrolysis voltage is 10-30 V, and the electrolysis time is 2-8 s.

9. The method for displaying a molten pool during selective laser melting according to claim 1, characterized in that: In step S14, observation and photography are performed using an optical microscope or a scanning electron microscope.

10. The method for displaying a molten pool during selective laser melting according to claim 9, characterized in that: The voltage of the scanning electron microscope was 15 KV, and secondary electrons were used to observe the sample and take pictures.

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